Time delay system



June 7, 1966 J. P. LIMON 3,254,871

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June 7, 1966 J. P. LIMON 3,254,871

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INVENTOR. JOSE E L /Mo/v BY @MQW TTO/PA/Eys United States Patent O "ice3,254,871 TIME DELAY SYSTEM Jose P. Limon, Rossford, Ohio, assigner toAuto-Tronic Control Co., Inc., Toledo, Ohio, a corporation of' hio Filedct. 31, 1963, Ser. No. 320,470 8 Claims. (Cl. 251-129) This inventionrelates to time delay means to delay inactivation of a load because of atemporary power interruption or fluctuation in current and morespecifically to a time delay unit for delaying the closing of acoil-operated gas supply valve when a temporary interruption orfluctuation of current occurs.

Industrial furnaces employing many gas-fired burners have gas supplyvalves which are designed to cut off gas flow to the burners if anelectrical power failure occurs. There yare several reasons for shuttingdown the burners in case of a power failure. For one thing, mostindustrial furnaces are equipped with complex safety devices which Iareinoperative in case of a power failure so that continued firing of thefurnaces would be without the benefit of such safety devices. Thecombustion air for the burners also may be supplied by a blower and thisair source will -fail yif the power does, thereby -allowing fuel gas tobe supplied directly into the furnace without air, if not shut off.Conveyors carrying products to be heat-tre-ated through the furnace alsoare usually electrically driven and, if the conveyor stops, pieces orproducts carried thereby may be overheated and ruined if the burners arenot shut down.

The principal difficulty with the operation of these coil- `oper-atedgas supply valves is that they will also close in the case of a brief,temporary power failure or even a current fluctuation. Such aninterruption or change in current would not, of course, be enough torequire shutting down of the furnace but, nevertheless, this occurs whenthe valve closes. Once the gas supply is c-ut off, each of the furnaceburners must be relighted 'and it is not infrequent that an industrialfurnace will employ twenty or thirty burners or more. In such aninstance, the time required for -relightiug is often substantial.Further, brief power interruptions or fluctuations will occur in someareas rather frequently so that a considerable amount of time may beexpended in restarting a furnace after a shut-down. yInaddit-ion, manyindustrial furnaces now employ heat-treating atmospheres of combustiblegases for various heat-treating processes such as carburizing, by Way ofexample. Although these gases are combustible, they are contained withinthe furnace chambers without air and under a slight pressure to preventair from entering. Consequently, the only place where comb-ustion ofthese gases can occur is Where they escape through .the openings in thefurnace and combine with atmospheric air. The only time such gaseouscombustible atmospheres are dangerous is if they are held `at atemperature below lapproximately 1400" F. since, if they are below sucha temperature, they will not burn even if combined with air.Consequently, an explosive mixture can form with this mix-turesubsequently exploding if brought into contact with Ian ignition pointor if once again heated to a temperature above approximately 1400 F. Asa result, if the furnace burners are shut olf due to a power 3,254,871Patented June 7, 1966 must be purged. Such periods of time may belengthy and result in substantial production loss during the period.

'The present invention relates to a time delay unit which c-an beelectrically connected with a gas supply valve to prevent closing ofthis valve in the event of a current tinctuation or interruption whichmay even bel up to several seconds in duration. When the new unit isincorporated with the valve, the valve will remain open for apredetermined period after a current failure and, if the current isrestored within the predetermined period oftime up to approximatelyseven seconds, for example, the gas valve will remain open continuously.

It is, therefore, a principal object to provide a time delay unit fordelaying the inactivation of an electrical load because of a temporaryinterruption or fluctuation in current.

Another object of the invention is to provide a time delay unit -for usewith `a :gas supply valve to prevent closing of the valve during currentuctuations or temporary power failures.

Other objects and advantages of the invention will be apparent from theIfollowing detailed description of a preferred embodiment thereof,reference being made to the accompanying drawing, in which:

FIG. l is a view in perspective of a time delay unit according to theinvention ready to be electrically connected to a coil-operated, gassupply valve or other load;

FIGURE 2 is a diagrammatic View of a time delay circuit embodying theinvention and incorporated in the unit of FIG. l, in combination with agas supply valve for controlling the flow of fuel gas to a plurality ofburners;

FIG. 3 is a diagrammatic view of a modified time delay circuit accordingto the invention;

FIG. 4 is a diagrammatic view of another slightly modiiied circuitaccording to the invention; and

FIG. 5 is another diagrammatic view of still another slightly modifiedtime delay circuit according to the invention.

Referring-to the drawings, and more particularly to FlG.'1, a time delayunit embodying the invention is indicated -at 10 and includes a suitablecasing 12 carrying electrical components connected into the furnacecontrol system and a gas supply valve by terminals indicated at 14. Theunit 10 is compact and lightweight and can be .added to almost anyexisting furnace control system and coil-operated gas supply valve.

Referring more particularlyfto FIG. 2, a coil-operated gas supply valveis indicated at 16 and includes a spring-loaded valve stern 18 extendingupwardly through an electro-magnetic coil 20 when the valve is open.When the coil 20 is energized, it holds the valve stem 18 in the openposition, thus permitting flow of gas through the valve 16. When thecoil is de-energized, the springloaded stern 18 immediately drops toclose the valve 16.

VIf any power failure occurs or, in some valves, even if there is acurrent fluctuation, the spring-loaded valve stem 18 will vimmediatelymove downwardly to the closed position when the coil 20 is temporarilyde-energized. Even if the power is restored quickly, the` valve willremain closed until the valve is manually opened by an operator. At thistime, all of the burners must be individually re-lighted and a largenumber of burners are often incorporated in a single industrial furnace.Further, all of the individual, manually-operated valves for the burnersmust be closed before the gas supply valve 16 is again opened, afterwhich the individual valves are opened one at a time as the burners arelighted.

Referring to the details of the circuit of FIG. 2, with lead lin'es 22and 24 connected to a suitable source of current, usually 110 volts AC., a control relay CR connected across the lead lines 22 and 24by lines26 and 28, will be actuated. This will close normally-open contactsCR-l, close normally-open contacts CR-Z, and open normally-closedcontacts CR-3. The closing of contacts CR-1 connects lines 30 and 32 tocomplete a circuit across the lead lines 22 and 24 along with additionallines 34, 36, and 38. This causes a capacitor C1 to charge with the aidof a diode D1 in series therewith which provides half-wave rectificationfor the A.C. current. At the same time, a second capacitor C2 betweenlines 40 and 42 is charged through additional lines 44, 46, 48 and 50through a second diode D2. A switch S connects the lines 48 and 50 forA.C. operation and will be discussed more fully subsequently. With thecontacts (2R-'2 closed, the coil 20 is connected across the lead lines22 and 24 by lines 52, 54, 56, 58, 60, 62, and 64 and is held in as longas there is power to the lines and the contacts CR-2 are closed.

If a power failure ora s ig-nicant power fluctuation should now occur,the current through the coil will immediately drop and, at the sametime, a capacitor C3 across thel coil by means of lines 66 and 67 willimmediately discharge to initially hold in the coil 20. At the sametime, the relay CR is de-energized to open its contacts CR-l and CR-2,thereby separating the capacitor C1 and the coil 20 from the powersource; the contacts CR-3 between lines 68 and 69 are also closed toconnect lines 48 and 56. This enables the capacitor C2 to quicklydischarge across the coil 20 thereby continuing to hold it closed. Also,the capacitor C1 can now discharge through a resistance R1 between lines70 and 72 which connect the lines 36 and 50. Because the capacitor C1discharges through the resistance R1, it discharges more slowly andprolongs the length of time in which the coil 20 remains energized dueto the discharging of the three capacitors C3, C2, and then C1. Byappropriately selecting the Values of the capacitor C1 and theresistance R1, the time in which the coil 20 remains energized after apower failure can be selected, a period of time from three to sevenseconds usually being desired. If the power should be restored duringthis period, the relay CR will again be energized to close its contactsCR-2 and thereby hold in the coil through power from the lines 22 and24. Again, the contacts CR-3 will be opened and contacts CR-l closed toenable the capacitors C1 and C2 to charge again.

On some gas supply valves, D.C. rather than A.C. coils are employed'.D.C. coils generally require less voltage than A.C. ones, but eithertype of coil can be energized through the time delay circuit of FIG. 2for short periods of time without harm. In the case a D.C. coil' isemployed with a D C. power source connected across the lines 22. and 24,the switch S is moved into contact with a line 74. In practice, a jumperwire can be used in place of the switch S for economical purposes sincethe use of a D.C. power source and coil are infrequent. In any event,with the lines 50 and 74 connected, the capacitors C2 and C1 will alwaysbe connected across the coil 20 regardless of the control relay CR whichis not needed with a D.C. power source to separate the capacitor C1 fromthe power source during discharging. Also in this instance, thecapacitor C3 and C2 willv discharge substantially together since thecapacitor C2 is always conected directly across the coil 20. Thecapacitor C1, however, will again discharge more slowly since it is still connected in series with the resistance R1.

FIGS. 3-5 show three modifications of the circuit of FIG. 2 with thecoil of the coil-operated gas valve being energized or held in upon apower failure or iluctuationy by a direct current power source in theform of a battery, rather than capacitors, with the connection of thebattery and, the coil controlled by separate means. In particular, thebattery is advantageous because it provides more reliable operation thancapacitors. Nickelcadmium lcells can be used for this purpose, being 4changed or re-charged every year to assure reliable operation.

Referring more particularly to FIG. 3, the coil 20 is connected to apower source through lead lines 76 and 78. A control relay CR also isconnected to the sou-ree of power throng-h lines 80 and 82 and isenergized with the coil 20. The contr-ol relay CR then closes itsnormally-open contacts CR-1 to connect lines 84 and 86. This connectscapacitors O1 and C2 across the lead lines 76 and 78 through connectinglines 88 and 90 and 94 and 96, respectively, and also by lines 98 and100, the lines 84 and 86, and lines 102, 104, and 106. The capacitors C1and C2 thereby are charged when the supply valve is normally open with ableeder resistance R1 beingv in parallel with the capacitor C1 and C2 bymeans of lines 108 and connecting the lead li'ne 78 and the line 98. Theresistance R1 tends to bleed 01T any excess charge on the capacitors C1and C2 to prevent overcharging.

When the relay CR is energized, it also opens its normally-closedcontacts CR-Z connecting lines 112 and y114 to prevent operation of ahigh-impedance pla-te relay PR connecting lines 1116 and 1,18. Avariable resistance. R2 is located between the lines 114 and 1x16 inseries with the plate relay PR to control its operation by controllingthe discharge of the capacitors C1 and C2 when the power source failsand the contacts CR-2 close.

The energization of the control relay also closes its contacts CR-3 toconnect the coil 20 with the power source. The contacts CR-3 open upon apower failure to separate the time delay circuitry from the powersource, during operation of the time delay system..

Finally, the control relay CR opens. its Contacts CR-4 when energized todisconnect the battery B from the coil during normal operation. Upon apower failure, the contacts CR-4 again close tol connect lines 120 and122 and complete a circuit fromthe battery to the coil through lines124, 126, 128, 130, 131, the lines 1Z0 and 122, and lines 132, 133, 134,136, 168, 140, and `142. During a power failure then, the coil 20 willremain energized by the battery B, providing that normally-open contactsPR1 between the lines 124 and 126 are closed. These contacts arecontrolled by the relay PR which,` in turn, is controlled by thecapacitors C1 and C2 and the Variable resistance R2. Thus, the battery Bsupplies thepower to keep the coil 20 closed during a power failurewhile the relayv PR and its contacts PR-1 control the time ofenergization of the coil 20. T-he relay PR also has normally-closedcontacts PR-Z toV separate this relay from the power source whenenergized by the capacitor.

A diode D1 between the lines 104: and 106 provides yhalf-wave rectiedcurrent for the capacitors C1 and C2. A second diode D2 between lthelines 126 and 128 prevents the possibility of the back of the coilv 20damaging thev battery which would be possible if the was sufficient tocause arcing across the contacts PR-1.

A capacitor C3 is connected across the coil 20 by lines 144 and 146 andserves to hold in the coil 20` after power failure and until theb-attery B can take over, aswell as to help prevent back of the coilfrom entering the rest of the circuitry. A fourth capacitor O4 isconnected across the lines and 140 by lines 148 and v to help absorbvoltage fluctuations in4 the. line. current which otherwise will affectoperation of the plate relay PR and thereby vary the time constant.4 Aresistance R3 between lines 152 and, 154 acts as, a bleeder resistancefor the capacitor C4 to bleed off any excess charge on the capacitor C4.

Another slightly modified time delay circuit is shown in FIG. 4, whichcircuit also employs a battery but uses a pneumatic timer. A controlrelay CR is connected across lead lines 156 and 158 by lines 1 60 and162. When current is applied, the relay CR is energized to close itscontacts CR-1 connecting lines 164 and 166 to complete a circuit withthe coil 20 through lines 168, 170, and 172. At the same time, contactsCR-2 of the relay CR are opened to disconnect lines 174 and 176 tomaintain a battery B disconnected from the coil 20. If the currentshould fail, the contacts CR-l will again open to disconnect ltheb-attery circuit from the main power circuit While the contacts CR-2will close to conne'ct the battery B to the coil 20 through a line 178,the lines 176 and 174, a line 180, the lines 168, 170, and 172 and lines182 and 184. C-urrent will thus be supplied to the coil to hold it inuntil the battery circuit is opened which occurs when a pneumatic timerT connected -between the lines 156 `and 158 by lines 186 and 188 timesout and opens its contacts T-1 between the lines 174 and 1-80. Thepneumatic timer T closes its contacts T-l when energized and maintainsthem closed until a predetermined period of time after the pneumatictimer is de-energized, this being up to seven seconds, for example. Thecontacts T-1 will then open and disconnect the battery from the coiluntil the timer T is again energized.

A d-iode D1 between the lines 176 and 178 protectsthe battery B fromback of the coil 20. A capacitor C1 between lines 190 and 1192discharges when the current fails to hold in 4the coil 20 until thebattery B can take over, and it also tends to absorb back from the coil.

The circuit of FIG. 5 is similar to that of FIG. 4,'

employing a pneumatic timer, but is designed particularly forcounterweighted valves or those employing heavier springs to cause fastclosing of them. In this instance, the coil 20 is connected across leadlines 200 and 202 and is actuated lwhen current is supplied throughthese lines. A control relay CR, which is preferably more sensitive thanits counter part in FIG. 4, is also connected across the lead lines 200and 202 by lines 204 and 206. The control relay CR has two sets ofnormally-open contacts CR-l and CR-Z which open when the relay isde-energized to separate the coil circuit and the battery from the mainpower source. The relay CR also has a third set of contacts CR-S whichconnect lines 208 and 209.

A pneumatic timer T between lines 210 and 211 operates in the samemanner as the timer of FIG. 4 except having the additional contacts T-2which separate the battery B from the main power source during normaloperationofthe coil 20 and which instantly close when the timer T isde-energized. When timer contacts T-l are closed, along with the secondtimer contacts T-2, a battery circuit can be completed from the batteryB through lines 212, 214, 216, and 218, the lines 208 and 209, and lines220, 221, 222, 224, and 226.

A capacitor C1 is located across the coil 20 by lines 228 and 230 to aidin holding in the coil and in absorbing back However, until the timercontacts can properly close to assure holding in the coil 20 by means ofthe battery B, a large capacitor C2 is employed between lines 232 and234 to complete a circuit for the coil 20 through the line 232, a line236, the lines 218, 208, 209, 220, 222, and 224, a line 238 and the line234. The battery B will then continue to energize the coil 20 throughits circuit until the contacts T-1 of the timer open.

Various modifications of the above described embodiments of theinvention Iwill be apparent to those skilled in the art, and it is to beunderstood that such modifications can be made without departing fromlthe scope of the invention, if they are within the spirit and the tenorof the accompanying claims.

What I claim is:

1. In combination with a main power source and a fuel supply valve forsupplying fuel to a plurality of burners of an industrial heat-treatingfurnace, said valve having a valve stem and an electrical coil to pullin said stem when energized and to open said valve when said coil isconnected to the main power source, means connecting said coil incircuit to said power source, means for continuing to energize said coilonly temporarily during a temporary power failure of said power sourcecomprising a separate, direct current power source in addition to saidmain power source, circuit means connecting said direct current powersource with said coil, a pair of contacts in said circuit means forconnecting and disonnecting said direct current power source and saidcoil, and means to open said contacts while said main power source holdsin said coil and to close s'aid contacts upon failure of said main powersource to connect said direct current power source and said coil totemporarily energize said coil.

2. For an electrical coil which is energized when connected to a mainpower source, means for continuing to energize said coil onlytemporarily during a temporary power failure of said power sourcecomprising a capacitor, circuit means for connecting said capacitor withsaid coil, a pair of contacts in said circuit means for connecting anddisconnecting said capacitor and said coil, and control means openingsaid pair of contacts when energized and closing said pair of contactswhen de-energized.

3. The combination according to claim 2 and a second capacitor, circuitmeans for connecting said second capacitor with said coil, and aresistance in series with the first capacitor to control the dischargethereof when said contacts are closed.

4. For an electrical coil which is energized when connected to a powersource, means for continuing to energize said coil only temporarilyduring a temporary power failure of the power source comprising abattery, circuit means for connecting said battery with said coil, apair of contacts in said circuit means for connecting and disconnecting.said battery and said coil, and means adapted to be responsive to thefailure of the power source to close said contacts temporarily duringpower-failure to connect said battery and said coil to temporarilyenergize said coil and otherwise to open said contacts to isolate thebattery from the coil.

S. The combination according to claim 4 wherein said last-named means isa timer which closes said contacts main power source when operative,means connecting said electrical `coil in circuit to said power source,means adapted to continue to energize said coil during a temporary powerfailure of the main power source comprising a direct current powersource, circuit means connecting said direct current power source inparallel with said Vcoil to said main power source, switch means foropening and closing said circuit means for connecting said directcurrent power sour-ce with said coil when closed and for isolating saiddirect current power source from the coil when open, and means to opensaid switch means when the main power source is operative and to closesaid switch means when the main Ipower source is inoperative thereby toconnect said direct current power source with said coil to temporarilyenergize said coil by discharge of direct current from said directcurrent power source through said coil when said main power source isinoperative.

8. In a combination with a main power source and an electrically-powereddevice normally operated through the main power source, means forcontinuing to operate the electrically-powered device during a temporarypower failure of the main power source comprising a direct current powersource, circuit means for connecting said direct current power source inparallel with said device to said main power source, switch means foropening and closing said circuit means between said direct current powersource and said device and adapted to connect said direct current powersource with said device when said switch means is closed and adapted toisolate said direct current power source from the device when saidswitch means is open, means energized by said main power source duringnormal operation of the device to open said switch means, andde-energized during power failure of said main power source to closesaid switch means thereby to connect said direct current power sourcewith the device to temporarily operate the device, and additional switchmeans connected in series with the device and said main power source,said additional switch means being operated by said energizing means,said ad# ditional switch means being `closed when said energizing meansis energized and opened when said energizing means is de-energized toisolate said device from the main power source when said direct currentpower source supplies current to said device.

References Cited bythe Examiner UNITED STATES PATENTS 2,958,811 11/1960Mungaard 158-28 2,982,351 5/1961 Scott 158-123 3,076,495 2/1963 Ray etal. 158-28 3,116,753 l/1964. Howe 137-4875 3,143,161 8/1964 Graves eta1. 158-28 3,153,440 10/1964 Baumanns 158-125 FREDERCK KETTERER, PrimaryExaminer. MEYER PERLIN, Examiner. M. L. BATES, Assistant Examiner'.

1. IN COMBINATION WITH A MAIN POWER SOURCE AND A FUEL SUPPLY VALVE FORSUPPLYING FUEL TO A PLURALITY OF BURNERS OF AN INDUSTRIAL HEAT-TREATINGFURNACE, SAID VALVE HAVING A VALVE STEM AND AN ELECTRICAL COIL TO PULLIN SAID STEM WHEN ENERGIZED AND TO OPEN SAID VALVE WHEN SAID COIL ISCONNECTED TO THE MAIN POWER SOURCE, MEANS CONNECTING SAID COIL INCIRCUIT TO SAID POWER SOURCE, MEANS FOR CONTINUING TO ENERGIZE SAID COILONLY TEMPORARILY DURING A TEMPORARY POWER FAILURE OF SAID POWER SOURCECOMPRISING A SEPARATE, DIRECT CURRENT POWER SOURCE IN ADDITION TO SAIDMAIN POWER SOURCE, CIRCUIT MEANS CONNECTING SAID DIRECT CURRENT POWERSOURCE WITH SAID COIL, A PAIR OF CONTACTS IN SAID CIRCUIT MEANS FORCONNECTING AND DISCONNECTING SAID DIRECT CURRENT POWER SOURCE AND SAIDCOIL, AND MEANS TO OPEN SAID CONTACTS WHILE SID MAIN POWER SOURCE HOLDSIN SAID COIL AND TO CLOSE SAID CONTACTS UPON FAILURE OF SAID MAIN POWERSOURCE TO CONNECT SAID DIRECT CURRENT POWER SOURCE AND SAID COIL TOTEMPORARILY ENERGIZE SAID COIL.